A coupling device has been developed in a direction of attenuating low frequency signals and improving high frequency signal characteristics since the coupling device generally used in a power system is used for the purpose of blocking power frequencies and delivering only a communication signal in a high frequency band. Further, in the case of a current transformer (CT) application, the CT has been developed in a direction particularly for improving the linearity to obtain an ideal B-H characteristic.
However, the characteristics of such coupling devices become meaningless when these coupling devices are used for power generation, and further the characteristic of attenuating the power frequency may be fatal to power generation. Accordingly, the power CT should be configured to have reverse characteristics to the existing CTs as follows;
(1) Power frequency characteristics should be maximized and other high frequency signals should be minimized. That is, the characteristic should be maximized in the frequency range below 120 Hz which is a doubled frequency of the power frequency of 60 Hz, and the characteristics should be minimized in the frequency range above 120 Hz to be as low as possible;
(2) The linear B-H characteristics required by a general CT is not necessarily required; and
(3) A general high saturation characteristic is not required, and rather a comparatively lower saturation characteristic by the required power energy is more effective. (an immoderate induction voltage in high power line current should be prevented) (see FIG. 1); and
(4) The existing CT manufacturing process should be used as it is, and should be realized even from low cost materials.
However, such conditions are quite appropriate characteristics for manufacturing the power CT but are reverse characteristics required by inductors, common CTs and the like, and therefore the manufacturing technology for common inductors or CTs may invite a big difficulty when it is used as it is for manufacturing the power CT having the desired characteristics.
That is, the high saturation induction characteristic is required in inductors or CT applications to enhance the linearity and to raise a signal to noise ratio in high frequency band, but on the contrary, since the high saturation induction characteristic rather generates an immoderately high induction voltage in high power line current, the separable CT causes many problems in treating the high induction voltage as is used as power source.
Meanwhile, since the power CT operates on an AC line, the shape of a magnetic flux density occurring in a general magnetic line also appears to be a sine wave form, and although occurring, a magnetic saturation is only a temporary phenomenon and does not involve a big problem in securing power source, but rather a high magnetic saturation generates a too high induced electromotive force, which may lead to difficulties in managing the generated power.
FIG. 1 is a graph of B-H curves showing preferred characteristics of a power CT. As shown in FIG. 1, unlike inductors or typical cores, the power CT exhibits higher characteristics than typical cores when a low current flows through a power line, and the power CT should have a characteristic not higher than that of inductors or typical cores when a high current flows through the power line in order to prevent an excessive induced voltage from occurring.
However, a number of various limitations are caused when the power CT is made of a magnetic alloy used for existing common inductors or CTs as described above.